Surface defect inspection method and apparatus

ABSTRACT

The present invention provides an apparatus and method which enable detecting a microscopic defect sensitively by efficiently collecting and detecting scattering light from a defect in a wider region without enlarging the apparatus. In the apparatus for inspecting a defect on a surface of a sample, including illumination means which irradiates a surface of a sample with laser, reflected light detection means which detects reflected light from the sample, and signal processing means which processes a detected signal and detecting a defect on the sample, the reflected light detection means is configured to include a scattering light detection unit which collects scattering light components of the reflected light from the sample by excluding specularly reflected light components by using an aspheric flannel lens and detecting the scattering light components.

This application is a divisional of U.S. patent application Ser. No.12/855,873, filed Aug. 13, 2010.

BACKGROUND

The present invention relates to a method and apparatus for inspectingfor defects on the surface of a substrate for a magnetic disk and asemiconductor wafer. In particular, the invention relates to a surfacedefect inspection method and apparatus suitable for optically inspectingthe surface of a substrate to detect dents and scratches on the surfaceand foreign matters attached to the surface.

An apparatus for optically inspecting for microscopic defects on thesurface of a substrate for a magnetic disk and a semiconductor wafer isrequired to carry out higher speed and more sensitive inspection. Toachieve more sensitive inspection, a method is adopted which includesincreasing the intensity of illumination light by using laser as a lightsource and detecting light reflected from the substrate and scatteringwith a high sensitivity sensor, as described in, for example, JapanesePublished Patent Application No. Hei 3-186739 and Japanese PublishedPatent Application No. Hei 5-21561. However, when the power or intensityof the illumination light is too strong, it will damage the substratesurface. Hence, reflected and scattering light from a defect on thesubstrate surface illuminated by the illumination light with limitedirradiation intensity has to be detected with maximum detectionsensitivity. As a configuration for detecting this reflected andscattering light with maximum detection sensitivity, the configurationadopting a photomultiplier unit is disclosed in Japanese PublishedPatent Application No. Hei 5-21561.

Scattering light from a microscopic defect has a characteristic inwhich, as the size of the defect becomes smaller, the amount of thescattering light from the defect per unit area decreases and thisscattering light is more likely to diffuse across the whole space abovethe defect. Therefore, it is necessary to efficiently collect and detectthe scattering light from the defect in a wider region in order todetect a microscopic defect sensitively using the illumination lightwith the same amount of light. To collect the scattering light in awider region (solid angle), this can be accomplished by using a largerobjective lens having a larger numeral aperture (NA) for collecting thescattering light from the substrate. However, employing a largerobjective lens having a larger numeral aperture is limited in practice,in order that the objective lens should be prevented from interferingwith other parts when installed in the inspection apparatus.

If a larger objective lens having a larger numeral aperture is employed,a converging lens through which the scattering light collected by theobjective lens converges on the detector plane of a detector has to belarger accordingly. A set of these larger lenses requires larger lensbarrels for supporting them, thus enlarging a detection optics systemand making it difficult to make the apparatus smaller and lighter.

SUMMARY

An object of the present invention is to provide a surface defectinspection method and apparatus which solve the above problem of theprior art and enable identifying a microscopic defect sensitively byefficiently collecting and detecting scattering light from a defect in awider region without enlarging the apparatus.

In order to achieve the above object, by using a structure combingaspheric flannel lenses or flannel lenses in a detecting optics systemof a surface defect inspection apparatus, the present invention enablescollecting and detecting scattering light from a defect in a widerregion, processing a detected signal, and identifying a microscopicdefect sensitively without enlarging the apparatus. It should be notedthat, in the following description, the invention will be describedtaking some examples where aspheric lenses are used for reasons ofexpediency, but the use of spherical flannel lenses can also provide asimilar effect.

Specifically, in an aspect of the present invention, apparatus forinspecting a defect on a surface of a sample is provided, includingrotatable and movable table means on which a sample is mounted, anillumination means which irradiates a surface of the sample mounted onthe table means with laser, reflected light detection means whichdetects reflected light from the sample irradiated with laser by theillumination means, and signal processing means which processes a signaloutput from the reflected light detection means by the detection of thereflected light and detects a defect on the sample, wherein thereflected light detection means is configured to include a scatteringlight detection unit which collects scattering light components of thereflected light from the sample by excluding specularly reflected lightcomponents by using an aspheric flannel lens and detects the scatteringlight components.

In another aspect of the present invention, an apparatus for inspectinga defect on a surface of a sample is provided, including a rotatable andmovable table means on which a sample is mounted, first illumination anddetection means which irradiates a surface of the sample mounted on thetable means with first laser and detecting reflected light from thesample, second illumination and detection means which irradiates thesurface of the sample mounted on the table means with second laser anddetecting reflected light from the sample, and signal processing meanswhich processes a signal output from the reflected light detection meansby the detection of the reflected light and detecting a defect on thesample, wherein the first illumination and detection means is configuredto include an illumination unit which irradiates the sample with laserand a scattering light detection unit which collects scattering lightcomponents of the reflected light from the sample irradiated with thelaser by excluding specularly reflected light components by using anaspheric flannel lens and detects the scattering light components.

In another aspect of the present invention, an apparatus for inspectinga defect on a surface of a sample is provided, including rotatable andmovable table means on which a sample is mounted, illumination meanswhich irradiates a surface of the sample mounted on the table means withlaser, reflected light detection means which detects reflected lightfrom the sample irradiated with laser by the illumination means, andsignal processing means which processes a signal output from thereflected light detection means by the detection of the reflected lightand detects a defect on the sample, wherein the reflected lightdetection means is configured to include a scattering light detectionunit which collects and detects scattering light components of thereflected light from the sample with the exclusion of specularlyreflected light components by using plural aspheric flannel lensesdisposed so as to surround virtually the whole surface above the tablemeans.

In a further aspect of the present invention, a method for inspecting adefect on a surface of a sample is provided, including mounting a sampleon a rotatable and movable table, irradiating a surface of the samplewith laser while rotating and moving the table, detecting reflectedlight from the sample irradiated with the laser, and processing a signalobtained by detecting the reflected light and detecting a defect on thesample, wherein the method is adapted such that detecting the reflectedlight includes collecting scattering light components of the reflectedlight from the sample by excluding specularly reflected light componentsby using an aspheric flannel lens and detecting the scattering lightcomponents collected by using the aspheric flannel lens by aphotoelectric converter.

In a further aspect of the present invention, a method for inspecting adefect on a surface of a sample is provided, including mounting a sampleon a rotatable and movable table, irradiating a surface of the samplewith first laser while rotating and moving the table, detecting firstreflected light from the sample by the illumination of the first laser,irradiating the surface of the sample with second laser while rotatingand moving the table, detecting second reflected light from the sampleby the illumination of the first laser, and processing a signal obtainedby detecting the first reflected light and a signal obtained bydetecting the second reflected light and detecting a defect on thesample, wherein the step of detecting the first reflected light includescollecting first scattering light components of the first reflectedlight from the sample by excluding specularly reflected light componentsby using an aspheric flannel lens and detecting the first scatteringlight components collected by using the aspheric flannel lens by aphotoelectric converter.

In a further aspect of the present invention, a method for inspecting adefect on a surface of a sample is provided, including mounting a sampleon a rotatable and movable table, irradiating a surface of the samplewith laser while rotating and moving the table, detecting reflectedlight from the sample irradiated with the laser, and processing a signalobtained by detecting the reflected light and detecting a defect on thesample, wherein the method is adapted such that detecting the reflectedlight includes collecting scattering light components of the reflectedlight from the sample by excluding specularly reflected light componentsby using plural aspheric flannel lenses disposed so as to surroundvirtually the whole space above the table and detecting the scatteringlight components collected by using the plural aspheric flannel lens bya photoelectric converter.

According to the present invention, it becomes possible to efficientlycollect and detect scattering light from a defect in a wider region;therefore, the invention enables detecting more microscopic defectssensitively as compared with the prior art.

According to the present invention, by efficiently collecting anddetecting scattering light from a defect in a wider region, sensitivedetection of more microscopic defects can be accomplished withoutenlarging the apparatus.

These features and advantages of the invention will be apparent from thefollowing more particular description of preferred embodiments of theinvention, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a schematic structure of a surfacedefect inspection apparatus according to a first embodiment;

FIG. 2A is a cross-sectional view of an aspheric lens;

FIG. 2B is a cross-sectional view of an aspheric flannel lens having thesame aperture as for the lens shown in FIG. 2A;

FIG. 3A is a graph showing an example of an output signal of a secondphotoelectric converter 37 in the first embodiment, representingdispersion in the intensity of reflected light from a region including amoderate convex defect;

FIG. 3B is a graph showing an example of an output signal of the secondphotoelectric converter 37 in the first embodiment, representingdispersion in the intensity of reflected light from a region including amoderate concave defect;

FIG. 4 is a front view of a display screen showing a GUI output exampleof an inspection result in the first embodiment;

FIG. 5A is a planar block diagram showing a schematic structure of aninspection apparatus according to a second embodiment;

FIG. 5B is a front block diagram showing a schematic structure of anillumination optics system 220 and a detection optics system 230 of theinspection apparatus according to the second embodiment;

FIG. 6 is a graph showing a range 601 in which defects are detected bythe detection optics system 230, a range 602 in which defects aredetected by a detection optics system 30, and a range 603 in whichdefects are detected by the combination of the detection optics systems230 and 30 in the second embodiment;

FIG. 7A is a plan view showing a schematic structure of an inspectionapparatus in a third embodiment; and

FIG. 7B is a front view showing the schematic structure of theinspection apparatus in the third embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Examples of embodiments of the invention applied to a defect inspectionapparatus for magnetic disks will be described below using the drawings.

Embodiment 1

FIG. 1 is a diagram showing an overall structure of a defect inspectionapparatus for magnetic disks according to Embodiment 1. The defectinspection apparatus is generally composed of a table section 10, anillumination optics system 20, a detection optics system 30, and asignal processing and control system 40.

The table section 10 includes a rotatable table 1 on which a sample 100is mounted and a stage 2 capable to moving the table 1 in a directionperpendicular to a principal axis of rotation.

The illumination optics system 20 includes a laser source 21 and aconverging lens 22 which converges laser emitted from the laser source21 on the surface of the sample 100.

The detection optics system 30 includes a first aspheric flannel lens 31corresponding to an objective lens which collects scattering lightcomponents of reflected light (specularly reflected light and scatteringlight) from the sample 100 illuminated by the illumination optics system20, a second aspheric flannel lens 32 corresponding to a converging lenswhich converges the collected scattering light, a first photoelectricconverter 33 (e.g., an avalanche photodiode (APD), a photomultipliertube (PMT), or the like) which detects the scattering light converged bythe second aspheric flannel lens 32 with high sensitivity, a mirror 34which reflects specularly reflected light components of reflected light(which includes specularly reflected light and scattering light) fromthe sample 100 and changes the light path of the specularly reflectedlight, a collecting lens 35 which collects the specularly reflectedlight whose light path was changed by the mirror 34, and a secondphotoelectric converter 37 with plural detector elements (e.g., aphotodiode array with plural pixels or an avalanche photodiode array)for detecting the collected specularly reflected light.

FIG. 2A shows a commonly used aspheric optical lens 310 and FIG. 2Bshows an example of an aspheric flannel lens 320 having the sameaperture as the lens 310. As can be seen from these figures, thethickness of the aspheric flannel lens 320 can be made relativelythinner than the commonly used aspheric optical lens 310 having the sameaperture. In the present embodiment, aspheric flannel lenses having thisfeature are used as the first aspheric flannel lens 31 and the secondaspheric flannel lens 32.

The signal processing and control system 40 includes a first A/Dconverter 41 which analog-to-digital converts and amplifies an output ofthe first photoelectric converter 33, a second A/D converter 42 whichanalog-to-digital converts and amplifies an output of the secondphotoelectric converter 37, a signal processor 43 which receives outputsof the first A/D converter 41 and the second A/D converter 42 andperforms signal processing on them, a storage unit 44 which storesresults of processing performed by the signal processor 43, an outputunit 45 with a display screen on which results of processing performedby the signal processor 43 are output, and an overall controller 46which controls the whole of the apparatus.

Then, the operation of each section/system is described. Controlled bythe overall controller 46, the table section 10 rotates the table 1 witha sample 100 mounted thereon and moves the stage 2 in a directionperpendicular to the principal axis of rotation in synchronous with therotation of the table 1.

While the sample 100 is rotated and moved by the table section 10, laseremitted from the laser source 21 in the illumination optics system 20being controlled by the overall controller 46 is converged on thesurface of the sample 100 by the converging lens 22 to irradiate thesurface of the sample 100.

From the surface of the sample 100 irradiated with laser, reflectedlight (including scattering light and specularly reflected light)arises, influenced by the surface condition, e.g., a defect or a scratchpresent on the surface and minute concavity and convexity (unevenness)of the plane. At this time, the scattering light is subjected todispersion depending on the size of the defect on the surface. That is,the scattering light from a large defect or scratch is subjected todirectional dispersion with relatively large intensity, whereas thescattering light from a small defect or scratch is subjected toisotropic dispersion with relatively small intensity.

Specularly reflected light components of the reflected light from thesurface of the sample 100 irradiated with laser are reflected by themirror 34 disposed (on the path of the specularly reflected light) atthe same outgoing angle with respect to the sample as the angle ofincidence of the incoming laser to the sample 100. The specularlyreflected light components are then directed to the collecting lens 35and collected through the collecting lens 35 to enter an imaging lens 36which forms the image of the specularly reflected light on the imagingplane of the second photoelectric converter 37. In this way, thespecularly reflected light components are detected (imaged) by thesecond photoelectric converter 37. The mirror 34 is formed to have asufficiently small shape so as not to reflect light components(scattering light components) other than the specularly reflected lightcomponents.

On the other hand, of the reflected light from the surface of the sample100 irradiated with laser, the light components (scattering lightcomponents) not reflected by the mirror 34, which entered the firstaspheric flannel lens 31 serving as the objective lens, are collected toenter the second aspheric flannel lens 32 serving as the converginglens. The scattering light components are then converged on the detectorplane (not shown) of the first photoelectric converter 33 and detectedby the first photoelectric converter 33 with high sensitivity.

Here, it should be noted that the first aspheric flannel lens 31 and thesecond aspheric flannel lens 32 are thinner and lighter thanconventional optical lenses. Thus, the lens barrels (not shown) withinwhich these lenses are mounted can be made relatively compact, ascompared with those for the conventional optical lenses. This increasesthe flexibility of design in terms of where these lenses should bedisposed above the sample and makes it possible to design the detectionoptics system with a numeral aperture (NA) of 0.6 or more (the NA islimited to 0.4 or less for the system when using the conventionaloptical lenses).

Since the scattering light from a small defect distributes isotropicdispersion above the substrate and the level of a detected signal isproportional to the area of the detector plane, the detection opticssystem of the present embodiment is able to obtain signal larger thanthe signal obtained by the same system using the conventional opticallenses when the detection sensitivity is comparable. In other words, thedetection optics system of the present embodiment is able to detectscattering light from a smaller defect than the conventional system,when compared at the same level of detected signal.

Each of the A/D converters 41 and 42 converts an analog signal outputfrom the first photoelectric converter 33 or the second photoelectricconverter 37 into a digital signal and amplifies and outputs the digitalsignal.

The digital signals output from the A/D converters 41 and 42 are inputto the signal processor 43. The signal processor 43 performs processingon the digital signals corresponding to both or either of the outputsignal from the first photoelectric converter 33 and the output signalfrom the second photoelectric converter 37. Thereby, the signalprocessor 43 detects a defect existing on the surface of the sample 100and locates the detected defect on the substrate 100, using informationfor a laser irradiation position on the sample 100 obtained from theoverall controller 47 which controls the table section 10. Further, thesignal processor 43 identifies the type of the detected defect, based onthe characteristics of the detected signals from the first photoelectricconverter 33 and the second photoelectric converter 37.

The detection optics system provided with the second photoelectricconverter 37 detects the specularly reflected light components from thesample 100 collected by the collecting lens 35. The second photoelectricconverter 37 may include plural detector pixels arranged in an array todetect a change and a deviation (dispersion) in the intensity ofreflected light from the sample 100 having a defect, if any, collectedby the collecting lens 35. FIG. 3A represents dispersion in theintensity of reflected light from a region including a moderate convexdefect and FIG. 3B represents dispersion in the intensity of reflectedlight from a region including a moderate concave defect. From thesegraphs, it is apparent that the intensity of the reflected light from aregion including a moderate convex defect decreases, whereas theintensity of the reflected light from a region including a moderateconcave defect increases.

Meanwhile, although not shown in FIGS. 3A and 3B, dispersion in theintensity of specularly reflected light from a region where a foreignmatter is attached to the surface of the sample 100 decreases like thedispersion in the reflected light from a region including a moderateconvex defect. However, the dispersion in this case is broader (i.e.,more elements in the array are used to detect the dispersion in thereflected light intensity) than the dispersion of specularly reflectedlight from a region including a moderate convex defect.

In this way, the dispersion of specularly reflected light from thesample 100 occurs in different manners depending on the type of adefect. By analyzing the characteristics of such dispersion of reflectedlight intensity, it is thus possible to identify a concave defect, aconvex defect, or a foreign matter. Using numerical information ofnumber of pixels of the first photoelectric converter 33 and the secondphotoelectric converter 37 which detect the reflected light from thesample 100, it is also possible to determine a rough size category(e.g., large, medium, small) of each defect detected.

Results determined by the signal processor 43 are stored into thestorage unit 44 in association with position information for a defect.In addition, these results are displayed in a map form 462 on the screen461 of the output unit 46 such that a defect(s) selected by a defectdisplay selector 463 can be identified according to type and size.

According to the present embodiment, scattering light frommicroscopically smaller defects can be detected, as compared with theconventional system. Taking an example of detecting a scratch defect,while the detection optics system using conventional optical lenses isonly able to detect a defect with a size on the order of several hundrednanometers (nm), the detection optics system according to the presentembodiment is able to detect a defect with a size on the order of onehundred nanometers (nm).

Further, according to the present embodiment, a compact detection opticssystem with a higher NA can be configured using the combination ofaspheric flannel lenses and it is thus possible to detect microscopicdefects without enlarging the apparatus.

Embodiment 2

As a second embodiment, an inspection apparatus equipped with pluraldetection optics systems as a combination of the optics system describedin the first embodiment and a conventional optics system is describedusing the related drawings.

FIG. 5A shows a plan view of a structure in which the illuminationoptics system 20 and the detection optics system 30 according to thepresent invention is combined with a conventional illumination opticssystem 220 and a detection optics system 230. Meanwhile, FIG. 5B shows afront view of the conventional illumination optics system 220 and thedetection optics system 230.

The structure of the illumination optics system 20 according to thepresent invention and the structure of the conventional illuminationoptics system 220 including a laser source 221 and a collecting lens 222are basically the same.

Outputs from both the detection optics system 230 and the detectionoptics system 30 are processed by a signal processor having a structurecorresponding to the signal processing and control system 40 describedin the first embodiment and a defect is detected. However, the structurecorresponding to the signal processing and control system 40 is omittedfrom FIG. 5B for simplicity and to avoid repeated description.

The detection optics system 230 of the prior art is configured such thatcomponents of light reflected from a sample 100 and passing through anobjective lens 231, i.e., reflected light (scattering light) componentswhose light path is not changed by a mirror 232 are detected by anphotoelectric conversion element 233. Meanwhile, specularly reflectedlight components from the sample 100 whose light path is changed by themirror 232 are collected by a lens 234 to converge on the detector planeof a light receiving element 235 and detected.

A relation between a laser irradiation position on the sample 100 by theillumination optics system 220 and a laser irradiation position on thesample 100 by the illumination optics system 20 is adjusted in advance.The sample 100 is illuminated by the illumination optics system 220 andthe illumination optics system 20 at the same time and respectivereflected lights from the sample are detected by the detection opticssystem 230 and the detection optics system 30. Respective signals thusdetected are confronted with each other so that detected signals fromthe same defect can be identified and processed, as their positionalrelation on the sample 100 is determined in the pre-adjustment step.

As a result, it is possible to combine a detectable range 601 (fromseveral hundred nanometers (nm) to several hundred micrometers (μm)) bythe detection optics system 230 with a detectable range 602 (fromseveral tens of nanometers (nm) to several hundred micrometers (μm)) bythe detection optics system 30, as is shown in FIG. 6. A range 603 inwhich defects can be detected by the apparatus as a whole can beextended as compared with a case where the detection optics system 230or the detection optics system 30 is used singly.

Embodiment 3

As a third embodiment, an example in which the apparatus is configuredsuch that virtually the whole space above a sample 100 is surrounded byaspheric flannel lenses described in the first embodiment is describedusing the related drawings.

Aspheric flannel lenses can be made of plastics and can be manufacturedinto an arbitrary form using plastic material. These lenses are lightbecause they are made of plastic material. When plural aspheric flannellenses are coupled and used, joint members for coupling them only needto have less strength than those that are used to couple ordinary glasslenses. Therefore, an assembly of aspheric flannel lenses can bemanufactured into a relatively thin structure.

To increase the sensitivity in detecting defects, as much scatteringlight from a defect as possible should be collected and detected by ahigh sensitivity photoelectric converter.

As already stated, scattering light from a defect has characteristics inwhich, as the size defect becomes smaller, the scattering light from thedefect is more likely to spread all directions above the defect. Hence,it is good for using an integrating sphere to collect this scatteringlight efficiently. However, the integrating sphere collects stray lightnear the surface together with the scattering light, which results in adecrease in the S/N ratio of detected signals. For commonly usedintegrating spheres, the reflectance of their inner wall does not reach100% completely and the sizes of an incident light window, an outgoinglight window, and a sample window result in a decrease in the lightcollection efficiency. Consequently, the total light collectionefficiency (the proportion of incident light at the detector in thelight reflected from a sample 100) decreases to 50% or lower.

Therefore, in the present embodiment, an assembly of plural asphericflannel lenses 731 to 742 having a polyhedral structure, as is shown inFIG. 7A (a hexahedron as in FIG. 7A), is used as an optics system thathas light collection efficiency equivalent to or higher than that of anintegrating sphere. And the optics system has a capability of detectinga defect from which directional scattering light is reflected andcollecting light scattered from a defect while excluding stray light.More specifically, an inner polyhedron which corresponds to an objectivelens is made up of aspheric flannel lenses 731, 733, 735, 737, 739, and741 and an outer polyhedron which corresponds to a converging lens ismade up of aspheric flannel lenses 732, 734, 736, 738, 740, and 742. Theaspheric flannel lenses 731, 733, 735, 737, 739, and 741 constitutingthe inner polyhedron are coupled with join members 761 and the asphericflannel lenses 732, 734, 736, 738, 740, and 742 constituting the outerpolyhedron are coupled with join members 762.

Because of the relatively thin structures of the joint members 761 and762, there can be a smaller area that shades scattering light from asample 100 to be detected and light collection efficiency of 80% can beensured. (For example, it is possible to form the inner and outerpolyhedral structures by cutting and forming a plastic sheet into theaspheric flannel lenses 731 to 741 and boding these plastic sheet lensestogether using a transparent adhesive agent.)

In this polyhedral assembly, laser emitted from a laser source 721,after passing through a collecting lens 722, passes through holes 743provided in top-plane aspheric flannel lenses 741 and 742 and irradiatesthe surface of a sample 100 in the central position of the polyhedralassembly. Specularly reflected light components of reflected light fromthe surface of the sample 100 pass through holes 744 provided in thetop-plane aspheric flannel lenses 741 and 742 and enter an objectivelens 735. Then, through an imaging lens 736, the image of the specularlyreflected light is formed on the imaging plane of a photoelectricconverter 737 and thus detected.

On the other hand, scattering light components of the reflected lightfrom the sample 100, diffusing across the whole space above the sample,enter the inner aspheric flannel lenses 731, 733, 735, 737, 739, and 741of the polyhedral assembly, disposed to surround virtually the wholespace above the sample 100, and are then converged through the asphericflannel lenses 732, 734, 736, 738, 740, and 742 constituting the outerpolyhedral structure which corresponds to the converging lens.

To the conjugate points of the respective aspheric flannel lenses 732,734, 736, 738, 740, and 742, one ends of glass fibers 751 to 756 areconnected, respectively, through which incoming scattering lightcomponents go out from the other ends of the glass fibers 751 to 756 anddetected by a photoelectric converter 757 with high sensitivityinstalled in front of the other ends of the gals fibers. By thusconnecting the one ends of the glass fibers 751 to 756 to the conjugatepoints of the respective aspheric flannel lenses 732, 734, 736, 738,740, and 742, it is possible to prevent stray light from entering theone ends of the glass fibers 751 to 756 and prevent the S/N ratio ofdetected signals from decreasing.

As a result of detecting scattering light by this photoelectricconverter 757, obtained signals are processed in the same way as in thefirst embodiment and, therefore, description thereof is omitted.

In the structure shown in FIGS. 7A and 7B, a subassembly of the inneraspheric flannel lenses 731, 733, 735, 737, 739, and 741 of thepolyhedral assembly and a subassembly of the aspheric flannel lenses732, 734, 736, 738, 740, and 742 constituting the outer polyhedralstructure are disposed so as to be spaced apart from each other.Alternatively, the subassembly of the inner aspheric flannel lenses ofthe polyhedral assembly and the subassembly of the aspheric flannellenses constituting the outer polyhedral structure may be disposed so asto contact each other.

In the present embodiment, the apparatus is configured such that the oneends of the glass fibers 751 to 756 are placed on the conjugate pointsof the respective aspheric flannel lenses 732, 734, 736, 738, 740, and742 and scattering light components entering the glass fibers 751 to 756are directed to the photoelectric converter 757 with high sensitivity.Alternatively, the apparatus may be configured such that, instead of theglass fibers 751 to 756, light shielding plates provided with pin holesto shade stray light may be installed at the conjugate points of therespective aspheric flannel lenses 732, 734, 736, 738, 740, and 742 andlight components passing through the pin holes of the light shieldingplates are detected by photoelectric converters with high sensitivitywhich are installed behind each of the shielding plates. In this case,six photoelectric converters are needed, but by processing their outputsseparately, it becomes possible to obtain information on scatteringdirectionality for each defect. It is possible to use such informationwhich is useful to improve the accuracy of classifying detected defects.

According to the present embodiment, by detecting scattering light froma sample 100 with relatively high light collection efficiency, it ispossible to obtain signals with a high S/N ratio, thereby enabling todetect microscopically smaller defects (several tens of nanometers ormore).

Although the examples in which aspheric flannel lenses are used havebeen described in the foregoing Embodiments 1 through 3, these lensesmay be replaced by spherical flannel lenses.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects allillustrative and not restrictive, the scope of the invention beingindicated by the appended claims, rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

The invention claimed is:
 1. An apparatus for inspecting a defect on asurface of a sample, comprising: rotatable and movable table means onwhich a sample is mounted; illumination means which irradiates a surfaceof the sample mounted on the table means with a laser; reflected lightdetection means which detects reflected light from the sample irradiatedwith the laser by the illumination means; and signal processing meanswhich processes a signal output from the reflected light detection meansby the detection of the reflected light and detects a defect on thesample, wherein the reflected light detection means includes ascattering light detection unit which collects and detects scatteringlight components of the reflected light from the sample by excludingspecularly reflected light components by using a plurality of asphericflannel lenses disposed so as to surround virtually the whole surfaceabove the table means, and wherein each said aspheric flannel lens has agreater numerical aperture than a conventional optical lens wheninstalling the conventional optical lens instead of said asphericflannel lens, and wherein the scattering light detection unit detectsthe scattering light components from a smaller defect than theconventional optical lens when installing the conventional optical lensinstead of said aspheric flannel lens.
 2. The apparatus for inspecting adefect on a surface of a sample according to claim 1, wherein thescattering light detection unit of the reflected light detection meansincludes a first set of said aspheric flannel lenses which are disposedso as to surround virtually the whole space above the table means andcollect scattering light components from the sample, a second set ofsaid aspheric flannel lenses which converge the scattering lightcomponents collected by the first set of aspheric flannel lenses, and aphotoelectric converter to detect the scattering light componentsconverged by the second set of aspheric flannel lenses.
 3. The apparatusfor inspecting a defect on a surface of a sample according to claim 2,wherein respective ones of said aspheric flannel lenses in the first setof aspheric flannel lenses are disposed so as to contact said asphericflannel lenses in the second set of aspheric flannel lensescorresponding to the respective ones of said aspheric flannel lenses. 4.The apparatus for inspecting a defect on a surface of a sample accordingto claim 1, wherein the reflected light detection means further includesa specularly reflected light detection unit to detect specularlyreflected light components of the reflected light from the sample.
 5. Amethod for inspecting a defect on a surface of a sample, comprising thesteps of: mounting a sample on a rotatable and movable table;irradiating a surface of the sample with a laser while rotating andmoving the table; detecting reflected light from the sample irradiatedwith the laser; and processing a signal obtained by detecting thereflected light and detecting a defect on the sample, wherein the stepof detecting reflected light includes collecting scattering lightcomponents of the reflected light from the sample by excludingspecularly reflected light components by using a plurality of asphericflannel lenses disposed so as to surround virtually the whole spaceabove the table and detecting the scattering light components collectedby using the plurality of aspheric flannel lens by a photoelectricconverter, wherein each said aspheric flannel lens has a greaternumerical aperture than a conventional optical lens when installing theconventional optical lens instead of said aspheric flannel lens, andwherein the step of detecting detects the scattering light componentsfrom a smaller defect than the conventional optical lens when installingthe conventional optical lens instead of said aspheric flannel lens. 6.The method for inspecting a defect on a surface of a sample according toclaim 5, wherein collecting the scattering light components by using theplurality of aspheric flannel lenses disposed so as to surroundvirtually the whole space above the table includes collecting thescattering light components from the sample by a first set of saidaspheric flannel lenses disposed so as to surround virtually the wholespace above the table, converging the scattering light componentscollected by the first set of aspheric flannel lenses by a second set ofsaid aspheric flannel lenses, and detecting the scattering lightcomponents converged by the second set of aspheric flannel lenses by thephotoelectric converter.